Advanced Debris-Flow Monitoring and Alarm System at Spreitgraben

After a rock avalanche in 2009, the Spreitgraben avalanche course in the Bernese Oberland,Switzerland, has experienced extremely erosive debris flows that pose an increasing threat toinfrastructure and residents.

Following first events, an extensive alarm and research system wasinstalled that is designed to alert residents and automatically close off the endangered cantonalroad. The alarm system is composed of several vertical trigger lines and gauge radars mountedabove the channel. Geophones provide a backup detection system in case of trigger linedisruption. Early warning data stems from a weather station and several webcams monitoringextended parts of the channel. Repeated terrestrial InSAR measurements provide informationabout rock instabilities in the starting zone on the northeast face of the Ritzlihorn.

To betterunderstand the process chain of the Spreitgraben debris flows, a third subsystem consists ofseveral research components. Two profile scanners constantly sample the channel cross sectionin order to investigate debris-flow dynamics. Additionally, two different models of Dopplerradar systems are being tested at the Spreitgraben site. These are aimed at an early detection ofdebris flows in order to prolong the warning time provided by the conventional warning system.

The entire system is connected to an extensive data transmission and information disseminationsystem that allows for continuous system monitoring and provides around-the-clock data accessto local authorities and decision makers.

Though 2012 and 2013 remained uneventful, the alarmsystem provided successful alerting throughout the debris-flow seasons of 2009 through 2011and provides valuable insight to debris-flow process understanding.